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Ways to correct for Atmospheric Dispersion in CMOS digital images?

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#1 rnyboy

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Posted 01 August 2020 - 02:34 PM

So I was making my second go for Jupiter and Saturn last night under better "seeing" conditions than last Friday and noticed that the different wavelengths of light were being dispersed along the vertical dimension in the two moons in the pasted in image at the bottom of this note.

 

I read about this artifact but never really thought about it until imaging Jupiter at f/20 with the 6SE and 2.5x GSO Barlow and REALLY seeing the color shift in those two moons,  I've seen it in the other images I've processed of Jupiter as a not too objectional issue along the top (blue) and bottom edges (red) of the planet but those moons should be mostly round and white.

 

I know there are Atmospheric Dispersion Correctors (ADC) that use two prisms to reconverge the wavelengths of light along the vertical dimension but then I thought since these are digital images there is probably a way to correct for it in some astronomy related software app I am unaware of.  I just started searching on this topic and really haven't found anything useful yet and I was wondering if any of you happen to know of any apps that are available that can "virtually" correct for this type of chromatic aberration?

 

Thanks for any feedback. 

 

0dHtbre.jpg


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#2 Peregrinatum

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Posted 01 August 2020 - 02:38 PM

if you have Pixinsight the ChannelMatch process can do this



#3 rnyboy

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Posted 01 August 2020 - 02:49 PM

Thanks for the fast reply.  I don't have PixInsight but I'll look into it.  I've only used AutoStakkert, Registax, or DeepSkyStacker with some PhotoShopping thrown in on my images so far.

 

I figured there had to be a way to do this given that it seems that any optical artifact exhibiting some type of order that can be described mathematically already has someone or multiple someones who have written a software app to minimize or mostly correct for the issue.  Optics has to be very high up there on the list of subjects that are extremely well understood from a mathematics POV.

 

Edit:  A PixInsight license costs nearly as much as my 6SE and if I had the scope setup to take advantage of PixInsight I'd get the license but hard to justify it at the moment.  Any other less pricey alternatives for ADC out there?


Edited by rnyboy, 01 August 2020 - 03:20 PM.


#4 bobzeq25

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Posted 01 August 2020 - 03:17 PM

You'll get more and better answers in the Solar System Imaging forum.



#5 ButterFly

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Posted 01 August 2020 - 04:07 PM

The software correction can only go so far.  Each image is captured with filters passing a band of wavelengths, typically RGB for planets.  There is dispersion within each of those bands because dispersion is  continuous.  The best that software can do is to align the RGB channels to each other.  Reconstructing the smearing within each band is not something that can be done with software.

 

Googling "ADC RGB saturn" returns some great results.  Here are some links with examples:

 

https://www.cloudyni...on-with-saturn/

http://skyinspector....-corrector--adc



#6 rnyboy

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Posted 01 August 2020 - 05:34 PM

Thanks bobzeq25 and Butterfly for the info.  I'll Google for the "ADC..." tomorrow.  



#7 KTAZ

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Posted 01 August 2020 - 05:44 PM

You are better off just buying the ADC. ZWO version is only $129. https://agenaastro.c...rector-adc.html

 

Here is an image I pulled last week on a pretty unsteady night with LOTS of atmospheric color shift:

TCyRSuI.jpg

 

No CA.


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#8 rnyboy

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Posted 02 August 2020 - 11:54 AM

Hi KTAZ.  Great image!  You maybe right, the price isn't too bad considering.  Do you do the adjustment while viewing Jupiter in real time?   If so I don't think I could do that because you can't see any AD in the real time images from my 6SE.  It's only after doing the post processing of the image that I can observe the AD.  Or do you used a nearby star at the at approximately the same elevation and adjust for minimal AD on that.  I'm just trying to figure out what the process would be on my 6SE since your C9.25 gives you a lot more light and detail to work with.

 

Edit:  I meant to add that I tried pulling out the individual R, G and B channels in PS E13 and then photomerging-composition to overlay the three channels as best I could over each other and then recolor balance.  It did improve moons so they appeared to show less dispersion in the color and were more uniformly white-ish and the blue fringe at the top and red fringe at the bottom of Jupiter were gone but I think the final image detail in Jupiter looked worse than in the starting image and I thought it would be better.  Here's the new overlaid RGB image (The colors aren't balanced the best but I was just trying to see what this approach could do)...

 

FvviTJV.jpg)


Edited by rnyboy, 02 August 2020 - 12:34 PM.


#9 APshooter

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Posted 02 August 2020 - 02:59 PM

Firecapture has a tool for aligning the prisms already in it. There are a few how to articles on how to use the feature. One has you aligning the red blue discs, another by upping the gain tool until you can actually see the red blue distortion on the planet itself and align the prisms to eliminate the red and blue fringing.

Edited by APshooter, 02 August 2020 - 05:23 PM.


#10 KTAZ

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Posted 02 August 2020 - 03:01 PM

As AP shooter mentioned, there is a nice tool integrated into FC to do the alignment realtime based on the image feedback.

#11 rnyboy

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Posted 02 August 2020 - 11:07 PM

I guess those are now on my list of things to do... learn how to use FC and buy a ADC.  



#12 APshooter

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Posted 03 August 2020 - 01:55 PM

There are several threads and a possible YouTube video on it.  Here's a thread from a few years back:

 

https://www.cloudyni...in-firecapture/



#13 prefetch

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Posted 03 August 2020 - 10:21 PM

You are better off just buying the ADC. ZWO version is only $129. https://agenaastro.c...rector-adc.html

 

Here is an image I pulled last week on a pretty unsteady night with LOTS of atmospheric color shift:

TCyRSuI.jpg

 

No CA.

 

"a pretty unsteady night"

 

if you think that jupiter image was taken on an unsteady night, i don't think you know what an unsteady night is.  lol.gif

 

that's an excellent image.  waytogo.gif




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